Recently, the characteristics of power electronic devices have been improved significantly. Power electronic devices with high-voltage rating, high-current rating, and high switching speeds have been developed due to the improvement of semiconductor manufacturing techniques. Power electronic devices are applied in electric power equipment, such as switching power supplies, uninterruptible power supplies, motor drivers, arc furnaces, trolley cars, battery chargers, lighting appliances etc. For example, converters are well known in the field of electronics, such as DC-to-DC, DC-to-AC, AC-to-DC or AC-to-AC converters. Such circuitry or devices are typically employed to convert one DC or AC voltage to another DC or AC voltage.
Typically, there are several kinds of power systems using the converters, such as a central power system (CPS) or a distributed power system (DPS). Referring to FIG. 1, FIG. 1 is a system block diagram showing a conventional central power system. In a central power system 10, a single input power source 11 is electrically connected to a power converter 12 and then to a plurality of loadings (RL) 13 (such as electronic devices). For example, the input power source 11 may be a DC power source, and the power converter 12 is employed to convert one DC voltage level to another DC voltage level. Therefore, the input power source 11 can supply power to the loadings 13. However, there are some disadvantages in the conventional central power system, such as high current stress on devices, poor reliability and difficulty in power maintenance, etc.
Referring to FIG. 2, FIG. 2 is a system block diagram showing a conventional distributed power system. In the distributed power system, a single input power source 21 is electrically connected to a plurality of DC-to-DC converters 22 and to a plurality of loadings (RL1, RL2, RL3) 23 (such as electronic devices), wherein the DC-to-DC converters 22 are electrically connected to the respective loadings 23, thereby supplying power to the loadings 23. Although there are some advantages in the conventional distributed power system, such as lower current stress on devices, supporting of N+1 redundancy, ease maintenance and customization with standardized module etc., yet when the single input power source 21 is broken-down or fails to supply power, the whole distributed power system would be useless.